Metal disintegrators are those which use an electric current to strike an arc between an electrode and a workpiece. A vibrator causes axial movement of the electrode and as the electrode retracts from the workpiece an arc is struck which dislodges a metal particle from the workpiece. As a hole is formed in the workpiece, feed means is provided to gradually move the electrode forward into the hole being formed. Coolant, usually water based coolant, is supplied to cool the electrode and carry away the chips being formed. Such metal disintegrators are used in salvage processes, for example, a partially formed workpiece may have a drill or tap broken off inside the workpiece. Rather than scrapping the workpiece a metal disintegrator is used to disintegrate the remaining portion of the drill or tap to salvage the workpiece.
An early proposal was to utilize an underwater electrical cutting electrode held to a metal workpiece by an electromagnet. Another early proposal was to remove a broken tap from a tapped hole in the workpiece wherein a special ring shaped support could be fastened to the workpiece and then an insulating guide on the ring support could provide axial guiding of a disintegrating electrode. In metal depositing rather than metal removing apparatus it has previously been proposed to vibrate an electrode in a portable unit. Also another proposal was a hand held unit wherein an electromagnet vibrated a disintegrating electrode. Still further, in electrical discharge machining of workpieces it is customary to provide a rigid but adjustable support for the electrode so that it may be guided and fed toward the workpiece. Such electrode supports were necessarily insulated from the workpiece for proper operation. Where the electrode is long, slender or otherwise transversely weak, it has been proposed to utilize an additional insulated guide near the working end of the electrode and supported from the machine structure.
The difficulty with the prior art constructions is that usually a large, heavy and rigid superstructure was required on the machine in order to rigidly but adjustably position the electrode properly for operating on a workpiece. Such adjustment mechanisms were often difficult to adjust easily and properly and to be sure that the workpiece was aligned with the aperture in the workpiece. Additionally, such distintegrators operated only with relatively movable workpieces which could be moved to the disintegrator machine. Where there were large or heavy workpieces and also where the workpieces were partially obstructed, such prior art disintegrators were unsuitable.
A special problem is how to remove defective rivets in a truck frame as the frame is being manufactured with the frame so large and unwieldy that it cannot conveniently be brought to a disintegrator machine. The problem is further complicated where the rivet to be removed is close to another frame member to be partially obstructed and in a location whereat the disintegrator electrode of a disintegrator machine cannot be aligned therewith. Accordingly the problem to be solved is how to construct a disintegrator which will operate on such large and partially obstructed workpieces.